Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$247.41	13.178%	$280.0137	$280.01	$280.00	$280.00
Purchase #2	$245.48	4.332%	$256.1142	$256.11	$256.10	$256.10
Purchase #3	$75.75	13.582%	$86.0384	$86.04	$86.05	$86.00
Purchase #4	$244.97	11.121%	$272.2131	$272.21	$272.20	$272.20
Purchase #5	$54.47	3.418%	$56.3318	$56.33	$56.35	$56.30
Purchase #6	$116.41	9.338%	$127.2804	$127.28	$127.30	$127.30
Purchase #7	$127.33	8.302%	$137.9009	$137.90	$137.90	$137.90
7 purchase totals =	$1,111.82		$1,215.8925	$1,215.88	$1,215.90	$1,215.80